Remove alarm (IPC) after traversal

To avoid an IPC on the main thread from blocking.

Test: observe trace (external/perfetto/tools/record_android_trace gfx
view freq sched wm am binder_driver -a com.android.systemui). There's
no blocking binder call on AlarmManager.remove during the updateDozing
transition.
Test: check DozeLog for time ticks
Test: atest DozeUiTest
Fixes: 236974182

Change-Id: I0d6d9dcbe89f769c9745936a6c91227a8f4c5288